What looks to be a fairly deep pool of cold air is expected to roar up over the next 2 days.BoM confident with thunderstorms for tomorrow evening and Friday with 2-15mm for tomorrow and around 10 mm for Friday. Local hail expected, more likely in the southern areas, some will make their way up to the Northern areas. 500HpA temperatures around the -28 to -32 mark so super cold up there, 16 for Adelaide Friday, Mt Lofty would no doubt be in single digits, not sure about snow there, slim chance, not very often but the system may be cold enough to deliver a very light dusting.

I reckon any storm wise activity will be a few flashes and rumbles from good sized clouds, mainly the ones associated with hail. Going up to 25mm from the total system.

A special fertilizer you sprinkle onto mountains or hills and wait for rain to water it in and wait about 5 months and watch it grow. That's how Mount Kosciusko grew.Such a crazy imagination I have haha.

Back on topic, looking like a nice pool of cold air and heavy showers with it on the Satellite, I think we will start seeing the start of it after 6pm at this stage. Still sticking with to 25mm by Sunday

I think 20-30mm is fairly possible they are not fast moving so showers including heavier fall may last bit longer than that. The shear this time seems bit more tame with only 20 knots or more not much in it. So they are just normal moving storm motion.

Going for 2mm for me amd thats very optimistic. BoM going for a few showers with a possible storm and small hail. Gotta laugh at that forecast. I would have thought they'd know by now that just doesn't happen in these setups. Fingers are crossed however for a southerly stream which will give us something =)

A special fertilizer you sprinkle onto mountains or hills and wait for rain to water it in and wait about 5 months and watch it grow. That's how Mount Kosciusko grew.Such a crazy imagination I have haha.

Brett Dutschke, Thursday May 1, 2014 - 12:44 ESTMuch of southern Australia is about to be hit by the strongest cold blast since last winter and strongest this early in the season in five or six years.

Some places may even be colder than any winter day in the past two years and possibly colder than any day this early in the season in more than 20 years.

Temperatures will drop as much as 10 degrees below the early May average and be as much as 25 degrees colder than what it was a month ago.

This will come as a shock to some, given it has been one of the warmest starts to autumn in many years in some areas.

This Friday and Saturday will feel like the coldest of winter days in South Australia, Victoria, the ACT, New South Wales and southern Queensland. Temperatures will struggle to reach the mid teens due to cloud and frequent showers. The wind will make it feel colder than 10 degrees at times.

Some showers will contain small hail and will fall as snow on some of the high country.

If Goulburn fails to exceed the forecast eight degrees this Saturday it will be its coldest day since winter 2011 and coldest day this early in the season in at least 20 years.

Mudgee, Griffith and Wilcannia may be colder on Saturday than on any day during last winter with forecast maximum temperatures of just 10, 11 and 14 degrees respectively.

The current forecasts also suggest Friday will be the coldest day this early in the season in six years in Adelaide with a maximum of 16 degrees and five years in Melbourne (14 degrees) and Canberra (11 degrees). This Saturday is forecast to be the coldest this early in the season in six years in Sydney with a top of just 17 degrees and 18 years in Logan in Brisbane with a high of 20 degrees.

The cold is developing as a result of a sharp tilt in the upper-atmosphere jetstream which is drawing cold air from the Antarctic as far north as the southern Queensland border. This airmass is originating from an area which has just experienced unseasonable cold itself. Casey station became a frigid minus 22 degrees on the Anzac long-weekend, seven degrees below its April average.

The most intense part of the cold pool will miss Tasmania and Western Australia, where temperatures will be a bit closer to normal.

Yeah I was going to mention the s**w word but I wasn't sure if it was out of the question or not... still... there's at least a small chance, I would think. Coincidentally, I'll be up at Mount Lofty on Saturday morning for breakfast (and also as a personal winter preparation test).

not necessarily... I'm yet to see actual forecast maps go that low over the Lofties and we have still got light flurries before. Really comes down to local conditions & timing. Also better to keep an eye on the 850temps than anything...

fwiw though, I agree its not going to be cold enough here on this occasion. Great sign though for the winter!

Yeah definitely Tim, doesn't look cold enough for high altitude, 850 temperature not low enough. But 700 low enough for hail yes. Its already developing showers. Access model forecast is spot on today well done BoM. Problem is most likely in cold pool it looks like no lightning at all, I think freezing level may have got far too low. But maybe not, later on if it goes further north into a bit warmer region then could go off with storms. But this front will be the best part where most thunderstorms will occur with higher level of freezing level. It is yet to form so will do so later after this first lots of showers this mid afternoon. Good news are it is not fast moving so it give you more longer rain from showers.

Generally you'd be wanting -4 or lower 850ies, with -2 being the absolute cut-off generally. We are going to be barely scraping 0 degrees with this, need the freezing level to drop by a good 500m or so IMO.

This however is a rather nice looking system for Thursday night into and through Friday. What is rather impressive is the Polar jet and VERY cold air ripping up from the south. Generally when I look at these, the troposphere is quite low and any convection will be capped at a relatively low level. However we have for a coldie type setup, relatively steep lapse rates deep into the atmosphere, generating some skinny CAPE, but when it comes to cold air, even a little bit of CAPE makes things interesting, so it's no surprise BoM have chucked possible storms into the precis. So rather tall coldies around I reckon, 500's dipping towards -30! Should be some nice dumps of hail around locally (well hopefully )I'll have a better look tonight at this, but a very interesting set up to come. SW streams will be cranking in the wake of it, will be some nice totals around.